This invention relates to an apparatus for measuring gobs of viscous liquid in free fall, particularly gobs of glass falling from the orifice of a glass feeder.
In the manufacture of glass articles, molten glass is first supplied to a gob feeder. This comprises a plunger which forces a molten stream of glass through an orifice where the gobs are separated with shears prior to falling into the hopper of a glass forming machine. In order to control the manufacture of the glass articles, it is important to monitor the weight and shape of the gobs of glass as they fall into the hopper.
One such method is described in U.S. Pat. No. 4,205,973. In this method the gobs fall through laser beams that activate perpendicularly arranged line cameras. These line cameras take successive scans as the gobs fall through their field of view. The successive scans are combined to determine the outline of the falling gob. The system requires careful synchronization of the camera scanning speed with the motion of the gob to ensure that a complete scan is obtained for each passage. A slight variation in the speed of the gobs will cause an error in the measured size since the difference between scanning lines on the image, for a given scanning rate, depends on the velocity of the gob. Furthermore, a separate camera is required for each gob position.